1. Field of the Invention
This invention relates to an imaging lens that forms an optical image of a subject on an imaging device, such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor), and to an imaging apparatus, such as a digital still camera, a cellular phone with a camera, a smartphone, a tablet terminal, and an information mobile terminal (PDA: Personal Digital Assistance), on which the imaging lens is mounted to perform photography.
2. Description of the Related Art
As personal computers became owned by many families and the like in recent years, digital still cameras, which can input image data of a landscape, a portrait and the like obtained by photography into the personal computers, have rapidly spread. Further, camera modules for inputting images became often mounted on cellular phones. Such equipment having an imaging function uses an imaging device, such as a CCD and a CMOS. As the size of the imaging device became small in recent years, the total size of imaging equipment and the size of an imaging lens to be mounted on the imaging equipment also need to be reduced. Further, since the resolution of the imaging device has become higher at the same time, the imaging lens needs to have high resolution and high performance. For example, the imaging lens needs to have performance corresponding to high resolution of 2 megapixels or higher, and desirably performance corresponding to 5 megapixels or higher.
To satisfy such need, for example, a five lens structure, which consists of a relatively large number of lenses, may be adopted to reduce the total length and to increase resolution (please refer to Japanese Unexamined Patent Publication No. 2009-294527 (Patent Document 1), Specification of U.S. Pat. No. 7,274,515 (Patent Document 2), Specification of U.S. Pat. No. 7,911,911 (Patent Document 3), Specification of U.S. Patent Application Publication No. 20100315723 (Patent Document 4), and U.S. Pat. No. 5,657,170 (Patent Document 5)).